Embedding process



UNITED STATES PATENT OFFICE. y

EDWIN L. WIEGAND, 0F PITTSBURGH, PENNSYLVANIA.

EMBEDDING PROCESS.

Specification ot Letters Patent.

Patented Nov. 29, 1921.

application mea :une a1, 1920. Hserial ne. 390,392.

ence being lhad to the accompanying drawhis invention relates to a novel process of embedding elements in impresslonable material, an example of its use being found in the production of electrical heating devices such as sad-iron, hot-plates, electric ranges, rheostats, and the like, for embed-` ding the conducting member or resistor element in a supporting and insulating matrix and for reducing the latter to its permanent and final condition. The objects Aof the invention arethe provision of a process of producing such devices which shall result in a final product of greater uniformity than heretofore, the avoidance of air pockets in the embedding material, and the securing of close contacts between such material and the resistor elements 'at all points; the provision of a process whereby the consistency of the embedding material can be more accurately controlled and its segregation prevented; the provision of a process which can be performed at higher speed, by more mechanical means, and with less reliance on the individual judgment and manual skill of the workman; the provision of a process wherein the steps follow each other immediately and without'intervening change in the conditions of temperature ormoisture; the securing of a better control of the amount of embedding material employed in connection with each unit; the provision of a process which facilitates the forming and embedding of large and massive elements; while further objects and advantages ofthe invention will become apparent as the description proceeds.

. In the drawings accompanying and forming a part of this applicatioml have illustrated certain apparatus and procedures whereb my improved process may be practised,.a though it Will be understood that I do not restrict myself to the precise steps or the precise order of such ste s or theexact apparatus herein set fort In these drawings, Fi re 1 is a perspective Vview of an empty sa iron base 'into which an element is to be embedded by means of my improved process; Fig. 2 represents the pre-- ferred mode of applying the embedding material thereto; Fig. 3. represents the second step, namely of leveling the surface of such material; Fig. 4 is a perspective view of the winding form with the resistance element in place thereon; Fig. 5 illustrates the third 1 ystep in the process, namely the inserting of the resistance element in the vembedding material; Fig. Gisa sectional view showing the element in place in the base; Fig. 7 illustrates the step of applying the final layer thereon; Fig. 8 the succeeding step of removing the excess material; Fig. 9 illustrates the final pressing or compacting; Fi 10 represents the step of drying; and ig. 11 the step of firing the dry unital I have chosen for illustration herein the construction of a common domestic sad-iron of the electric type, although this is intended as typical of the manufacture of any electrically heated or yother device to the making of which my'` .process is adapted'.

The heating element is contained in a hollow@ metal' shell or casing which here takes the form of the sad-iron baseand is formed with a Hatl bottom 1 and a surrounding Wall 2. The central boss herein illustrated is used solely for the purpose of attaching the top parts of the iron and has no part in the present invention excepting to indicate how conveniently my process adapts itself to irregularities and special conditions. I irst preferably moisten the interior of the recess by dipping "or spraying with Water, and

`then having emptied out all the Water which will wur therefrom I set the base upright and ll it full of embedding material lightly 'fsifted thereon from the sieve'3. While I do not restrict myselfI to any single embedding material, I referably employ one consisting essentia ly of granular a uminum oxid as -a base mixed with a small amount of binder which is ordinarily some kind of refractory clay. In general that material is chosen which exhibits the highest possible electrical resistivit at the different working temperatures or which the apparatusv is designed and Which shows the minimum decline in resistivity with increase of temperature, I prefer to use a binder that will mature orto some extent v itrify at the firing temperature and Vat the same time possess after iring'anfele'ctrical resistivity equal to that of tlie base. In quantity the binder and granular base should be so proportioned -that the percentage of binder will be the minimum necessary to secure a completely graded mixture and to produce a finished unit with the necessary mechanical propit to be mesh of a erties and a minimum of porosity. I preferably employ a granular base of about 180 mesh and with this I `find that from aboutl l impressionable state, being uniformly mixed with air so -as to form a soft mass.

'. As soon' as the entire base has been thus Aloosely filled to overflowing with the sifted material, I level off the top by means of a scraper as Vshown in Fig. 8, leaving-a light,

uniform, porous, damp mass of embedding material indicated at'4. I now set this base upon the platen 5 of a hydraulic or other suitable press and b 'means ofthe movable member 6 .thereof insert the resistor elevment 1n .the material and simultaneously compact said material so as to expel the air and firmly;l retain the resistor.l In order to efl'ect'this the resistor, generally in the form of al flat ribbon wire 8, is wound vupon a series-'of 979 of a form ofthe nature shown in my earlier Patent No. 1,133,347,

- and illustrated Vherein conventionally by the block'or die 10 adapted' for application to the ,member 6 of the press.- Between the resistor and the ace'of the block or diethere is interposed the movable stripper, late 12 which '1s aperturedfor the pins. hel die 10 and presspart 6 areequip'ped with means, such asiron rod 13, which when forcedl against the stripper plate shall prevent it from accompanying the die when the latter is raised, thereby removing the resistor from the pins and leaving it embedded in the material 4 as shown in Fig. 6. In this lway the resistor is first introduced into the -embed- 5 ding material when thejlatter is uniformly soft and impressionable,'whi1e the comparatively.v small amount of water 'containedv in that material, coupled with thehigh pressure obtainable by the press, enables the same to be compacted so solidly as to secure a very close and heat-conducting contact at every point both of the base and ofthe wire,

. and to hold 'the latter firmly in Vplace even though-it possess a large amount of resiliency. Subsequent to me raising of the die, the stripper plate i's removed.

l 'The upper edge of the resistor is however still exposed and the withdrawal of the pins 9--9` has lett` a number of small cavities 15--15 adjacent the conductor which if not y filled might produce hot spots in the latter and thus shorten its life. Accordingly, the base is again illed to overflowing withmore of the same disintegrated material as shown in Fig. 7, after which theexcess is removed by a scraper as shown in Fig. 8, and the material is finally compacted by the use of a plain die 16 operatedbetween the platen 5 and plunger 6 of a hydraulicor other suit-l able press as shown in Fig. 9.

The unit is then transferred to a suitable drying oven where it is subjected to a gradual heating, and beginning with a temperature below boiling and rising verly slowly to a temperature of 400J to 500 rather small sizeof the grains employed and preferably a. current of air As a result of the the high pressure with which they are compacted the porosity of the mass is very small,

Awhich ne essitates the removal of the water very 'gra ually and without any such heating as ywould tend todisrupt the integrity of the mass or open additional pores. The

time consumed .for this drying operation depends upon the size and thickness and porosity ofthe unit and generally requires at .least five to-ten hours even with a small unit. When the highest temperature is reached the elements are .transferred to a 4 high temperature oven for the final firing. Preferablybetween these two steps the elements are tested electrically to ascertain the condition oft' the insulation and the presence of any appreciable moisture, but I prefer not to allow the elements to cool appreciablyA at this period. The final firing is4 effected at the lowest temperature at which the binding material will become properly matured or partially vitrified but within the limit set by the nature of the' various substances comprising the unit. It will be understood that the embedding material is not lnecessarily thoroughly vitrified by this operation inasmuch as the manner in which the embedding material is affected at the .permissible temperature depends primarily upon the nature of the embedding'material employed and onl secondarily upon the operation performe After cooling the units are ready to receive the different attachments generally employed therewith.

As 'material'for the resistance unit, for application where the element is fired or used at a temperature of 1000 F. or over where exceptional durabilityl is desired, I

prefer to use one of the chromium alloys,

such as chromium and nickel, or chromium and iron although forv applications where more moderate temperatures are encountered a lsimple nickel-steel alloy is frequently'suflil cient. I prefer to use these resistors in press, since'for sma l articles a common hand` press is sufiicient. My improved process is not restricted to sad irons but is equally applicable to electrical devices of allkinds operating wholly or partly on the conducting principle, for example contact and surface heaters, hot plates, electric ranges, melting pots, rheostats, etc., besides having application to things not electrical, when it is desired to embed an element in impressionable material. I do not restrict myself to a sifting of the embedding material into the .casing inasmuch as the same result is secured in case the material is pre-sifted (or otherwise mixed uniformly with air) and then introduced into the casing in any suitable manner. I do not restrict myself to the use of the same kind of'insulating material above the resistor as is employed beneath the same, nor to its introductionl in the same manner as the first portions even when the same kind of material is used. My improved process is not limited to any one kind or nature of embedding material although to comply with the statutory requirements l have described one which will work perectly but without intent to restrict myself thereto or in any other wise except as specifi-- call recited in my claims.

aving thus described my invention, what l claim is y l. The processl of producing an electrical heating element which contains the steps of first, introducing into a suitable receiver a uniformly impressionable mass of non-fluid embedding material, second, introducing into said mass a previously formed resistance element and simultaneously subjecting the mass to high pressure so as to compact the same and hold said resistance element in place, third introducing additional embedding material to cover said resistance element, next drying the mass, and finally bringing the same to a stable condition by the application of heat.

2. The process of producing an electrical heating element which contains the steps of preparing a non-fluid mixture of a liquid and a granular electrically non-conducting material which is insoluble therein, disintegrating said material and mixing the same with air so as to produce a uniformly impressionable mass, introducing into said mass a previously formed metallic resistance element, and compacting'said mass under pressure to expel the air and integrate the material.

3. The process fof producing an electrical heating elemet which contains the steps of preparing a non-Huid mixture of a liquid and a granular electrically non-conducting material which is insoluble therein, disintegrating said material and mixing the same with air so as to produce a uniformly impressionable mass introducing into said mass a previously fprmed metallic resistance element, and simultaneously compacting said mass S'o as to expel the air and embed said resistance element firmly in the solidified material. v

4. The process of supplying a receiving casing with an electrical heating element which contains the steps of first preparing in said casing a uniform non-fluid mixture containin liquid, gas and solid components each yof w -ich is insoluble in the other, and

the solid component being. a non-conductor of electricity, introducing into said mixture a previously Jormedresistance element and simultaneously subjecting the same to a s ufiiciently high degree of pressure to expel the gaseous constituents, and force the solid constituents into close contact with the element, the casing walls and each other, removing the liquid portions by evaporation, and curing the solid constituents by the aid of heat.

5. The process of forming an electrical heating element inside a receiving casing, which contains the stepsot` first dampening with liquid a pulverized, insoluble, embedding material, second, sifting the dampened material into the empty casing so as to produce therein a uniformly impressionable mass containing a considerable amountV of air, introducing into said mass a previously formed resistance element, and afterward subjecting the mass to pressure whereby the air is expelled and the embedding material compacted into close contact with the casing and element.

6. The process of making an electric heating element which contains the steps of forming a resistance wire into a predetermined shape characterized by the possession of spaced, naked, turns, submerging such formed Wire in a slightly moistened embedding material which has been rendered uni-4 formly impressionable by grating through a sieve, and afterward subjecting the mass to a uniform pressure whereby the embedcling material is compacted between and around said turns.

7. 1n the process of making an electric to expel the air and introduce the solid por-V tions thereof uniformly between and around said Wires. v

8; The process of making an electric heating element which contains the steps of first producing an `intimate uniform mixture of pulverized electrical "insulating, heat conducting refractory material, binding material, Water, and air, introducing therein a strand of metallic resistor, compacting said mass so as to expel the airand cause it to embrace closely said resistor, drying said element ata 'low temperature until the Water is expelled, and finally raising the temperature sutliciently to mature and stabilize the binding material.

9. The hereindescribed process which comprises the steps of preparing a non-fluid 'mixture *of a liquid and a granular material signature. EDWIN L. VVIGrAND.` 

